void main(){
  double a=10;
  a??=5;
  print(a);

  var b;
  b??=10;
  print(b);

  a+=2;
  print(a);
  a-=b;
  print(a);
  a*=b;
  a/=b;
  a%=b;
  print(a);
  b~/=b;
  print(b);
}
